Apparently, Catalyst's book was set up to benefit from declines in the market, as well as sideways and slow up moving markets. The fund's Achilles heel was a rapidly rising market. What is now readily apparent in hindsight is that Catalyst's book was net short gamma in way out of the money calls. Probably, somewhere between 5% and 10% out of the money, through the sale of February 1x4 or 1x5 call spreads. That's a buy of one call and the simultaneous sale of four or five higher strike calls. In a market that isn't moving, this part of the position will slowly decay and expire worthless, adding return to the fund through the collection of time premium. In a rapidly rising market, this is a huge problem as the fund becomes shorter and shorter as the market rises, generating increasing losses. These trades, according to some traders, left the fund short more than $15 billion SPX deltas.